This invention relates to a liquid level indicator for detecting and indicating the levels of a variety of liquids such as gasoline, oil, petroleum and water in various containers such as tanks provided for automobiles, industrial machines, etc., and more particularly, to the core of a coil which is provided in the liquid level detecting section of the liquid level indicator.
A float arm type or linear potentiometer type liquid level indicator in which a potentiometer is operated by a float arm, an induction type liquid level indicator in which the variation in inductance of a coil is utilized, and many other types of liquid level indicators are available in the art. Of these conventional liquid level indicators, the induction type liquid level indicator is the most excellent in measurement accuracy.
Some of the present inventors have proposed an induction type liquid level indicator in which a conductive ring with a float is put on a coil in such a manner that it is movable on the outer circumferential wall of the coil, and the variation in inductance of the coil with the movement of the conductive ring is converted into a variation of voltage so that the level meter is operated. In the case of this liquid level indicator, in order to increase the variation in inductance of the coil thereby to increase the liquid level detecting sensitivity, it is desirable to provide a core inside the coil.
In order that the variation in inductance of the coil is caused only by the movement of the conductive ring with the winding component of the core itself released, it is preferable that the core is made of a magnetic material electrically insulated. A typical example of the core thus made is a ferrite core. However, if the core is made of such an electrically insulated magnetic material, (1) because of the electrical insulation the coil has a stray capacitance which distorts the coil voltage. (2) In order to cancel the stray capacitance, it is necessary to provide a suitable means. (3) Since the core is formed by pressing as in the case of forming a ferrite core, it is necessary to provide different metal molds respectively for cores different in length. (4) Long cores are liable to be curved or broken because they are low both in moldability and in mechanical strength.